Motorized variable path length cell for spectroscopy

ABSTRACT

The present invention is thus directed to an automated system of varying the optical path length in a sample that a light from a spectrophotometer must travel through. Such arrangements allow a user to easily vary the optical path length while also providing the user with an easy way to clean and prepare a transmission cell for optical interrogation. Such path length control can be automatically controlled by a programmable control system to quickly collect and stores data from different path lengths as needed for different spectrographic analysis. Moreover, the system utilizes configured wedge shaped windows to best minimize the reflections of light which cause periodic variation in transmission at different wave lengths (commonly described as “channel spectra”). Such a system, as presented herein, is able to return best-match spectra with far fewer computational steps and greater speed than if all possible combinations of reference spectra are considered.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of and claims priority to pendingU.S. patent application Ser. No. 13/975,693, filed Aug. 26, 2013,entitled “Motorized Variable Path Length Cell for Spectroscopy,” whichapplication is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the field of spectral analysis and,more specifically, toward the identification of the type and quantity ofdifferent chemicals in solid (e.g., soft) and liquid samples bytransmitting light of varying wavelengths through the sample so as toprovide wavelength information and to provide measured amounts of lightabsorbed by any given sample.

BACKGROUND OF THE INVENTION

Discussion of the Related Art

A molecular spectrometer is an instrument wherein a solid, liquid, orgaseous sample is illuminated, often with non-visible light such aslight in the infrared region of the spectrum. The light transmittedthrough the sample is then captured and analyzed to reveal informationabout the characteristics of the sample. As an example, a sample may beilluminated with infrared light having a known intensity across a rangeof wavelengths, and the light transmitted by the sample can then becaptured for comparison to the light source. Review of the capturedspectra can then illustrate the wavelengths at which the illuminatinglight was absorbed by the sample. The spectrum, and in particular thelocations and amplitudes of the peaks therein, can be compared tolibraries of previously obtained reference spectra to obtain informationabout the sample, such as its composition and characteristics. Inessence, the spectrum serves as a “fingerprint” for the sample and forthe substances therein, and by matching the fingerprint to one or moreknown fingerprints, the identity and the quantity of the sample might bedetermined.

However, there are numerous occasions when the data collected using suchabove described methods is useless because the transmitted light issubstantially absorbed by too large of a path length, or the light isnearly totally transmitted by too small of path length. Either one ofthese situations can be problematic. With respect to a large absorbance(e.g., due to a large path length), uncertainties based on noise (i.e.,signal-to-noise) become problematic as the spectral signal of the sampleis lost due to the light being too weak to be reliably detected within alarger signal. However, if the absorbance signal is too small (e.g., dueto a small path length), reliable detection is still a problem alsobecause of a lack of absorbance signal strength even though overalllight level is high. By varying the path length through the sample, bothof these problems can be minimized. Other uncertainties in bothsituations also can include natural variations in the light intensitycaused by dirt, dust in the light beam, temperature, vibrationvariations affecting the measurement means, and/or finally statisticalvariation the light source and detection system.

Background information on an apparatus and methodology that provides formeasuring optimized absorbance properties of a liquid droplet can befound in U.S. Pat. No. 7,365,852, to Schleifer, issued Apr. 29, 2008,entitled; “Methods and Systems for Selecting Pathlength in AbsorbanceMeasurements,” including the following: “[m]ethods and sub-systems forsubstantially optimizing the absorbance measurement in opticalinstruments are provided. A method comprises forming a liquid sampleinto a droplet extending between opposing surfaces, passing a light beamthrough the sample, and varying the distance between the two opposingsurfaces until a distance substantially corresponding to a optimumaborbance is obtained.”

Background information on an apparatus and methodology that provides formeasuring transmission properties of liquids and solids can be found inU.S. Pat. No. 7,582,869, to Sting et al., issued Sep. 1, 2009, entitled;“System and Method for Optical Analysis,” including the following: “[a]noptical analysis system utilizing transmission spectroscopy foranalyzing liquids and solids includes a source of optical energy, asample, a movable optical energy transmission window, a fixed opticalenergy transmission window, and a detection system. The fixedtransmission window remains fixed relative to the source of opticalenergy. The sample is selectively positioned between the movable andfixed optical energy transmission windows for analyzing the sample. Theoptical energy is transmitted through one of the windows, the sample,and the other window to obtain encoded optical energy as a result oftransmitting the optical energy through the sample. A detection systemreceives the encoded optical energy for analysis. The movable opticalenergy transmission window is selectively movable relative to the fixedoptical energy transmission window to repeatedly and precisely align andmake readily accessible both windows and the sample.”

Background information on an apparatus and methodology that provides formeasuring transmission properties of compressed samples can be found inEP 1, 792, 653, to Juhl, issued Jun. 6, 2006, entitled; “Apparatus andmethod for spectrophotometric analysis,” including the following: “[a]napparatus for spectrophotometric analysis comprises a sample receptionsurface, which is arranged to receive a sample to be analysed, and asample contacting surface, which is moveable in relation to the samplereception surface such that it may be brought to a first position, wherethe surfaces are sufficiently far apart to allow the sample to be placedon the sample reception surface, and a second position, where the samplecontacting surface makes contact with the sample and compresses thesample. The apparatus further comprises a sample thickness controller,which is arranged to control the distance between the sample receptionsurface and the sample contacting surface in the second position of thesample contacting surface, such that a sample thickness between thesurfaces may be shifted for obtaining at least two measurements of thesample at different optical path lengths through the sample.”

SUMMARY OF THE INVENTION

The present invention is directed to an automated system and method ofvarying the optical path length in a sample that a light from aspectrophotometer must travel through. In particular, the presentembodiments described herein allow the user to easily vary the opticalpath length over a large range typically from about 5 microns up to10,000 microns while providing the user with an easy way to clean andprepare a transmission cell for optical interrogation. Such varied pathlengths can be automatically manipulated by a programmable controlsystem to quickly collect and store data from different path lengths asneeded for different spectrographic analysis.

Thus, an aspect of the present application includes an apparatus formeasuring an optical property of a sample that includes: a first windowand a second window; wherein the first window is configured to receiveradiation from a source of optical energy over free space and the secondwindow is configured with an incorporated optical detector that isutilized to optically interrogate a disposed sample therebetween thepair of windows, and wherein the first window and the second window areboth moveable with respect to the positioning of the source of opticalenergy, and wherein the surfaces of the first window and the surfaces ofthe second window are further configured to respectively provide a firstoptical wedge and a second optical wedge so as minimize channel spectra;and wherein a processor is adapted to control a separation betweenconfigured surfaces of the first window and the second window at avariable distance (P) in order to pull the disposed sample into a columncontained by surface tension or to squeeze the sample during opticalanalysis, wherein the processor is additionally configured to collectand store information of different optical path lengths automatically ofthe pulled and/or squeezed sample(s).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary infrared (IR) apparatus.

FIG. 2 shows an exploded view of the optical mechanical components usedto provide IR transmission measurements.

FIG. 3A shows the general concept of manufacturing a low cost off-centerconical “wedge” via the utilization of a larger window.

FIG. 3B and FIG. 3C show the general concept of manufacturing a numberof smaller low cost off-center conical “wedged” windows out of a singlemanufactured part.

DETAILED DESCRIPTION

In the description of the invention herein, it is understood that a wordappearing in the singular encompasses its plural counterpart, and a wordappearing in the plural encompasses its singular counterpart, unlessimplicitly or explicitly understood or stated otherwise. Furthermore, itis understood that for any given component or embodiment describedherein, any of the possible candidates or alternatives listed for thatcomponent may generally be used individually or in combination with oneanother, unless implicitly or explicitly understood or stated otherwise.Moreover, it is to be appreciated that the figures, as shown herein, arenot necessarily drawn to scale, wherein some of the elements may bedrawn merely for clarity of the invention. Also, reference numerals maybe repeated among the various figures to show corresponding or analogouselements. Additionally, it will be understood that any list of suchcandidates or alternatives is merely illustrative, not limiting, unlessimplicitly or explicitly understood or stated otherwise. In addition,unless otherwise indicated, numbers expressing quantities ofingredients, constituents, reaction conditions and so forth used in thespecification and claims are to be understood as being modified by theterm “about.”

Accordingly, unless indicated to the contrary, the numerical parametersset forth in the specification and attached claims are approximationsthat may vary depending upon the desired properties sought to beobtained by the subject matter presented herein. At the very least, andnot as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, each numerical parameter shouldat least be construed in light of the number of reported significantdigits and by applying ordinary rounding techniques. Notwithstandingthat the numerical ranges and parameters setting forth the broad scopeof the subject matter presented herein are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical values, however, inherently contain certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements.

General Description

The embodiments described herein are contemplated to provide opticalinterrogation of samples, such as, but not limited to, solids, softsolids, and liquids that include oil-based samples. The length of thetransmission path of the light through a given sample varies over a widerange depending on the given sample and the type of measurement that isneeded. The present embodiments described herein are thus designed toprovide the user with a high degree of control over one or more pathlengths in real time and automatically. The beneficial result of such anovel aspect is that by collecting and storing many data sets ofdifferent path lengths automatically, later analysis of the stored datacollected is possible at many different path lengths.

Another beneficial aspect of the embodiments described herein is thatthe configuration also provides an easy means to allow the user to placea small sample (typically a drop of a sample) on a sampling window inthe light beam for analysis, which naturally allows for the easy removaland cleaning of the sample from the sample cell windows to enable rapidanalysis of many samples in a short amount of time.

Specific Description

Turning now to the drawings, the apparatus, as illustrated in FIG. 1 andgenerally designated by the reference numeral 100, shows a rotationalarm configured to be in an “open” position in which a sample of a solid(soft pliable samples) (not shown) or reference solid sample can beapplied or a drop of analyte or reference sample (not shown), (e.g.,samples of less than about 2 μl, oil based samples, liquid samples,),can be dispensed or aspirated onto a lower surface of a configuredwindow 5′. As discussed in more detail below, such an “open” positionenables easy access to the ends of the surfaces, e.g., desired surfaceconfigurations for optical windows 5 and 5′, so as to apply any of thegiven samples and enable a user to easily clean such surfaces providedon windows 5 and 5′, and to mount a new sample within the apparatus whendesired.

Thereafter, upon the application of a sample, the arm 4 of apparatus100, as shown in FIG. 1, is angularly moved by a user to be in the“Operating”, i.e., closed position (as often sensed by position sensor(not shown)), so as to result in the desired surface of window 5 to bebrought into contact with a desired sample contained therebetweensurfaces provided by windows 5 and 5′. Such a configuration enables, forexample, a surface tension mode (i.e., pulling sample into a column) ora mode that enables “squeezing” the sample via the configured surfacesof windows 5 and 5′. In either of these example modes, it is to beappreciated that the apparatus 100 shown in FIG. 1 can thereafter, asdescribed hereinafter, collect and store many data sets of differentpath lengths automatically and thus provide later analysis of the storeddata at the many, if needed, different path lengths.

Turning back to FIG. 1, the closed “Operating” position is aided by themechanical coupling of a hinge rod 6 configured therethrough bores inboth the swing arm 4 and in a hinge spacer block 6′, with hinge spacerblock 6′ being rigidly fixed with respect to base plate 2. In addition,a detector casing 7, which can include, but is not strictly limited to,a light detector 7 and window 5 coupled to swing arm 4, also mustnecessarily rotate about hinge rod 6 to enable a surface of window 5 tocome into contact with a sample provided on an upper surface of window5′. It must be noted however, that while samples can often be providedon the upper surface of lower window 5, it is to also be appreciatedthat given samples can also be applied to the lower surface of upperwindow 5 in some instances. If that is the desired mode of operation,the sample is then angularly rotated via arm 4 to come into contact withthe desired surface of lower window 5′without departing from the workingembodiments described herein.

The present embodiments thus allow the user to easily change from onesample to a different sample by having a moveable pair of windows (5 and5′) that pass a broad range of light wavelengths. Such windows 5, 5′allow a wide range of liquids (e.g., oils) and some solids to be placedinto a light beam for spectral analysis. These windows 5, 5′ arearranged in an opposing manner. Moreover, the lower window 5′ is oftenbonded to a large flat surface (e.g., sample platform 3) to present theuser with a sufficient area that can support samples that can vary insize and type. The upper window 5 can be bonded to the aforementionedmoveable arm 4 that can be raised (e.g., rotated away) to allow theplacement or removal of a sample and then lowered to the sample tocollect spectral data. The sample can, as an example, be a thin pliablesolid but is typically a liquid as such a media allows the path lengthto be varied and is therefore a desirable sample type although theapparatus shown in FIG. 1 and as described herein can of courseaccommodate non-liquid samples as well.

As an example design for illustrations purposes only, the presentinvention provides for two windows that are at a minimum dimension ofabout 5 microns (0.005 millimeters (mm)) up to a maximum dimension of upto 50,000 microns (50 mm) to give an adequate area to bond the window attheir edges and additionally have dimensions that are easy and low costto manufacture.

The detector 9 is often but not necessarily coupled (e.g., integrated,incorporated) to the upper window 5 because it is desirably small andlight weight allowing the arm to be easily lifted so that the user canclean and inspect the windows quickly. Example infrared (IR) detectorsthat can be implemented herein include, but are not limited to,deuterated triglycine sulfate detector (dTGS), Lithium tantalate(LiTaO₃), Triglycine sulfate (TGS), Indium gallium arsenide (InGaAs),Germanium (Ge), lead sulfide (PbS), Indium antimonide (InSb), Mercurycadmium telluride (MCT), and Mercury zinc telluride (MZT) detectors.

The upper arm 4, as shown in FIG. 1, is designed so that it is easy tolift and swing (rotate) back to a position where the user can easily seethe bottom surface of the upper window 5. The arm 4 and window/detectorassembly has an upper position (e.g., the “Open” position as shown inFIG. 1) wherein it is held in place by a resilient mechanism (not shown)(e.g., a spring), or a magnetic means (e.g., an electromagnetic orpermanent magnet), so that the user can use both hands to clean andinspect the upper window. At the same time the lower window 5′ isoperationally uncovered so that the lower window 5′ can also be easilycleaned and inspected.

The light source 12 can be configured from a number of known designs,such as, but not limited to an incandescent lamp, an ionized gas lamp, alaser, a light emitting diode, etc. to provide desired electromagneticradiation. Preferably, the source 12 is configured to provide theoptical energy over free space to a desired optical window describedherein (e.g., a lower window 5′). The optical bandwidth provided by thesource 12 can be over any desired wide range of wavelengths or narrowbands of wavelengths but often the source is designed to provideinfrared light from about 1 micron up to about 25 microns. As is oftendesired, such IR light can be modulated for Fourier transform infraredspectroscopy (FTIR) interrogation. In addition, such IR sources, oftenbeing larger and especially when coupled to desired optical focusingmeans (not shown) are thus designed to be located below and/or to theside of the lower window 5′. Such components can however, be designed tomove but are often designed to be fixed for convenience.

The sample arm 4 has a repeatable mechanical stop, e.g., in the form ofpin (not shown) or hinge 11, that provides a desired position againstwhich the lower surface of the arm 4 abuts when the arm is rotated so asto provide for the contact and measurement of a sample. Such aconfiguration provides for a repeatable down (active) position relativeto the light source optics which directs the upward traveling light (seereference characters 8) towards a repeatable dimensional location (e.g.,a focal point). This is the same repeatable location that the detector 9has when the sampling arm 4 is in the lower position, as shown inFIG. 1. As discussed above, a resilient mechanism, e.g., a spring, or amagnetic means, e.g., electromagnetic or permanent magnet, can be usedto provide extra force to holding down the sampling arm 4 in arepeatable location as the data collection is done.

FIG. 2 shows a more detailed view of the transmission cell section ofthe optical arrangement and is now referenced to provide clarity of theembodiments herein. Thus, FIG. 2 shows a disclosed arrangement,generally designated by the reference numeral 200 that includes a sampleplatform 3, the respective upper and lower windows 5 and 5′, thedetector case 7, and detector 9. Also generally shown is an opticalsource 12, often an IR optical source, and even more often an IR sourceto provide a modulated IR beam for FTIR as known to those of ordinaryskill in the art, as briefly discussed above. However, while FTIR is adesired embodiment so as to operate in the near-infrared as well as themid-infrared regions, it is to be appreciated that the presentconfigurations can also be configured with other near-infrared tomid-infrared spectroscopic systems and should not be construed to belimited to FTIR systems solely.

Turning back to FIG. 2, a resultant transmission cell is shown having aplurality (often two) of windows 5 and 5′, often thin diamond windows,configured with special surfaces (to be discussed below) and anadjustable mechanism 14 (e.g., a motorized (stepper-motor)), which iscoupled to sample platform 3 (as shown in FIG. 1), to adjust the spacebetween (i.e., to adjust optical path lengths) the two windows 5 and 5′(also to be discussed in detail below). From such a configuration,adjustable lengths over the range of about 5 microns up to 10,000microns are provided by the system shown in FIG. 1.

Again referring to FIG. 2, as an example mode of operation, the lightbeam typically travels vertically up through the windows 5 and 5′ andcan travel at other angles if desired by the user through software ormanual control. Since the light detecting means (e.g., detector 9) aretypically smaller than the light sourcing means (e.g., light source 12),the light is normally directed up (see reference characters 8 anddenoted accompanying directional arrows) toward the detection means(e.g., detector 9) to allow the design of the small light weightdetector 9 to move with the upper window 5 in the sample arm 4 thattravels or swings up and or away from the lower window 5′ where thelight enters the contained sample. Nonetheless, the source can also beconfigured in the swing arm with the detector positioned below ifdesired although such an arrangement is not optimal. However, thepreferred moveable detector configuration via mounting arm 4 allows boththe upper and lower windows 5, 5′ to be accessible for both loading newsamples and cleaning any old samples that might be adhering to eitherupper or lower sample windows 5, 5′.

The light detector 9 incorporated is often designed to be substantiallysmall dimensionally not only to operate at sample temperature but toalso beneficially place the detector 9 very close to the upper window 5in the moveable arm 4 and use proximity focusing as a mode to eliminatethe need for detector focusing optics. As an alternative arrangement, ifthe detector 9 operates at a different temperature than the interrogatedsample, the example embodiments provided herein enable detector transferoptics (not shown) to be incorporated to allow the detector 9 to befarther away from the sample in a known fashion. A simple ellipticalmirror, for example, can be utilized to enable placing the detector 9father from the sample to allow heating or cooling the sample totemperatures that the detector 9 cannot tolerate otherwise.

The light path through the transmission sampling system originates froma light source means 12 (e.g., an IR light source, such as a modulatedIR source), which can include one or more light sources and fixed orvariable filtering means (not shown) to create a light source 12 thatresults in both light intensity and light wavelength information. Thelight from the source 12 is directed to a focusing means that caninclude any known configuration of refractive, reflective componentsthat can operationally direct the light through the first window (e.g.,lower window 5′) supporting the sample and then therethrough the secondwindow (e.g., upper window 5), so as to be collected by a lightdetection means (e.g., detector 9). It is to be appreciated that it ispossible in some cases that part or all of the wavelength filteringmeans (not shown) can be placed in the light path after the sample andwindows 5, 5′. However, while the above configuration is beneficial, amore desired optical configuration is to have the light source 12,variable filtering/interferometer and focusing means (not shown), whichare typically larger than the light detection means placed near or underthe sampling window 5. Thus, the light created is focused in a upwarddirection through the windows 5, 5′ and sample onto a light detectionmeans 9 that is in a known standard location relative to the lightsource 12 and focusing means that is known to those skilled in the art(not shown). Moreover, it is to also be appreciated that while FIG. 1shows the apparatus having light source 12 under platform 3 as coupledto window 5′ and the light detection means 9 (e.g., photometric orspectrophotometric radiation detector) coupled to arm 4, it is to bestressed that another example embodiment can include arm 4 beingconfigured with the light source 12 (e.g., a photometric orspectrophotometric source) and the platform 3 arranged with lightdetection means 9 (e.g., photometric or spectrophotometric radiationdetector).

It is to be appreciated however that since the light detector 9 is oftensmaller in a desired fashion than the light source 12, as discussedabove, it is thus convenient to place the light detector 9 near theupper sample window 5 in the illustrated moveable arm 4 that can belifted up and away from the lower sample window to facilitate the user'saccess to the sample location. This allows the user to inspect bothwindows so that the user can know that the windows are clean and readyto accept a sample.

As a benefit of this arrangement, the user can, if desired, lower theinspected clean/cleaned upper window 5 and light detector 9 to thestandard known location of the apparatus 100, as shown in FIG. 1, tocollect a standard “Background” spectrum with no sample in place toverify the entire spectrometer system and to store a referencebackground spectrum for later use. It is to be appreciated however thatit is also possible with many samples to eliminate the background datacollection step and just use a Beers law and mathematical model toextrapolate over many different path lengths to build a backgroundspectrum of virtual zero path length, as to be discussed below. In anyevent, the user can then raise the up window 5 and easily place a sampleonto the lower window 5′.

As another example beneficial and novel embodiment, window 5′ can belowered by a computer (processor) controlled motor (e.g., see referencecharacter 14 of motor, as shown in FIG. 1) approximately, for example,by up to 1 millimeter to increase the sample path length before theupper window 5 is lowered to its standard sampling location. This allowsthe path length to be shortened (i.e., squeezed) as data collectionproceeds. This example process of “squeezing the sample” allows highviscosity samples to be run without worry that air introduced into thelight beam as the windows 5, 5′ are separated.

Maintaining the light detector 9 and window 5 in a known locationrelative to the light source 12 is important so that a given opticalpath length between the upper window 5 and lower window 5′ can bedetermined with confidence about the acquired data and stored with thespectral data. In essence, the detector 9 and window location placementenables the changes in sample type and thickness to be measured withoutconcern that the directed light (e.g., the focus of the light beam) haschanged due to changes in the detector 9 location relative to the lightsource optics (e.g., focusing means (not shown)). This is importantbecause relative motion between the light source optics (not shown) andan example light detector 9 can cause a change in the amount of thelight collected by the detector 9 and if left unchecked, produce anerroneous change in apparent light absorption of the sample if thedetector location changes between different sample and backgroundreference data collection scans.

Therefore the upper sample window 5 and detector 9 are often, but notnecessarily, only moved to two repeatable positions in the presentembodiments. The up position allows the users to remove, clean, inspect,and place samples on the sample windows, and the down provides a fixedfocus and known optical path length during the collection of background(no sample reference) and sample scans.

Turning back to FIG. 1, lower sample window 5′ is coupled (e.g., viabonding) to a flat sampling platform 3. It is to be appreciated thateither of the windows 5, 5′ and/or alternatively, the sample platform 3can be treated with a material (e.g., a hydrophobic, a hydrophiliccoating) known by those of ordinary skill in the art to prevent overspreading of an applied liquid drop analyte (e.g., oil) or referencesample (e.g., to stop spreading of an applied sample at the confines ofthe sample platform 3). The platform 3 design itself however, is alsoconfigured to prevent any liquid sample from running away from thesample window(s) 5, 5′ location and dripping over the edge of thesampling platform 3 into the supporting mechanism and optics below thesample window(s), 5, 5′ and platform 3. Moreover, such a large platform3 enables many different samples to be placed between the windows 5, 5′.To further prevent leaking of the sample (not shown), the sampleplatform 3 is often of solid construction and has no perforations (e.g.,holes, slits, etc.) where a desired sample can flow or leak down underthe sample platform 3. As an added arrangement, the sampling platform 3surface can be, but not necessarily, surrounded by a lip or wall tocontain liquid samples if large amounts of sample were accidentallyplaced in the sampling area.

As another feature, the sampling platform 3 can also be mounted on ahinge if the hinge is a large distance (e.g., at least 60 millimeters)from the window to limit the angle of tilt as the window is raised andlowered. This fact also allows a single piece of stainless steel to actas the sample platform 3 to hold the lower window 5′. This single partcan be fixidly mounted to the base of the system if more than 60millimeters away from the window. Another arrangement includes the useof a thin flexible surface platform 3. In particular, the natural flexin a thin piece of metal, such as, but not limited to stainless steel,can operate as a hinge, with a benefit that there are no gaps for liquidsamples to leak though the hinge area down into the light source meansand other mechanism mounted underneath the same sample platform 3.

The sample platform 3 is also capable of being mounted on (i.e., coupledto) the adjustable mechanism 14 (e.g., a computer controlled elevator,such as, a motorized (stepper-motor)), for the purpose of varying thesample path length between the two sample windows. Such an adjustablemechanism 14, (e.g., a motor) can be controlled by a manual switch or bya computer program. A preferred embodiment of the invention is however,software controlled motor 14 that can automatically vary the distancebetween the sample windows to control the light path length through thesample in a programmed way to facilitate the measurement of theabsorption spectra of many different samples.

As shown in FIG. 1, the adjustable mechanism 14 can, as one beneficialconfiguration, include a linear actuator 16 with, for example a motorconfigured as the adjustable mechanism 14 secured to the base plate 2 bymeans of fasteners, such as, for example, screws, posts, pins, rivets,etc. The use of a motor 14 in such an arrangement thus provides arotational motion of the linear actuator 16 to cause lift to or to lowerthe sample platform 3. Preferably, the travel distance and/or positionof the linear actuator 16 or any elevator/lowering means incorporated ismonitored during operation of the apparatus 100, as shown in FIG. 1. Asan added arrangement, movement of the motor 14 and/or platform 3 caninclude a reference position sensor (not shown) that establishes a“home” or reference position when the motor control system initializesupon startup or interrupted by, for example, an opto-interrupter device(not shown).

Through such a motor/software controlled arrangement, the entire sampleplatform 3 can, when in the proper position, be moved up and down, forexample, by about 5 microns up to 10,000 microns to change the samplepath length as needed. In a desired embodiment, the lower sample window5′ via coupling to the sample platform 3 can be programmed to stay inthe lower location so that the user can clean, inspect and collectbackground data. Only after a sample is loaded and data collection isstarted is the program going to move, e.g., raise the sample window5′/platform 3 to reduce optical path length as needed.

The sample platform 3 can thus be programmed to stay in the lowerposition all the time until the sample arm 4 is lowered to protect, forexample, configured diamond windows 5, 5′ from damage caused by thesample arm 4 being inadvertently forced down rapidly. In particular,such a rapid and inadvertent movement can, if not prevented, enablehitting the stop with enough speed and force to bend/deflect the arm 4and support systems enough to force example configured diamond windows5, 5′ together with enough force to damage them. Thus, a desired methodof the present application is to provide that only after the sample arm4 is lowered into a sampling position is the motor drive enabled todirect the sample platform 3 up to produce small optical path lengths.However, as soon as the arm 4 is lifted, the motor 14 drive is directedto lower the sample platform 3 enough (e.g., lowered up to 1000 microns)to make damage unlikely.

It is to be noted that with most samples it is possible to first raiseand then lower the sample platform 3 a plurality of times with windowand surface tension nonetheless keeping a liquid sample in place. Onlyhigh viscosity semi-solid samples are limited to a squeeze only to avoidair bubbles. It is also to be noted that the present embodimentsdescribed herein are designed to provide surface tension modifyingcoatings to be added to the sample platform 3 to aid in keeping thesample on the window rather the spreading out on the sample platform 3.These coatings allow the same sample to be run at different path lengthsover a number of repeated data collection cycles and aid in the use oflow viscosity samples. Different coatings are thus used with differenttypes of samples to aid the user in quickly and accurately placing asample on the lower window 5′.

Turning back to FIG. 2, the windows 5 and 5′, which can be coated (e.g.,anti-reflection (AR) coated) on desired surfaces to increase lightthroughput, are mounted above and below each other. The light 8 travelsup from the light source via configured optics (not shown) that arebelow the lower window 5′ to detector 9 which is mounted as close as isreasonably possible to the upper window 5. By placing the detector veryclose to the upper window (e.g. to within microns) the need for anyoptics between the detector and the upper window is eliminated.

In a desired arrangement, the upper window 5 is often a diamond windowof about 200 microns at its thickest point thick although window 5 isnot limited to just such a thickness. The detector 9 is often but notnecessarily mounted at about 1000 microns up to above 500 microns abovethe upper window 5. The lower window 5′ is also often but notnecessarily a diamond window of about, but not necessarily 200 micronsat its thickest point. Thin windows, when diamond is the material, areimportant to reduce cost, reduce diamond phonon absorption, and toreduce distance from the detector to the bottom surface of bottom windowbut again, the present embodiments described herein are not to belimited to just thin windows.

As disclosed herein, the preferred windows have configured surfaces toprovide wedged optical components. Such components are designed tominimize or even substantially eliminate the reflections of light whichcause periodic variation in transmission at different wavelengths (i.e.,commonly known to those skilled in the art as “channel spectra”). Aprevious application, i.e., U.S. application Ser. No. 13/931,348,entitled: “MOTORIZED VARIABLE PATH LENGTH CELL FOR SPECTROSCOPY,” toCoffin et al., of which is incorporated by reference in its entirety,teaches window geometries that address spectral channeling. However, thepresent window geometries are superior to the aforementioned applicationwith respect to minimizing or even eliminating spectral channeling andare thus a focus of the present invention. In particular, the surfacesthemselves provide for a pair of wedged optical windows that each bestscramble the reflections internal to each optic, the result of whichaids in the minimization of the aforementioned “channel spectra”problem.

It is to be appreciated, however, that a problem of light reflecting offof the surface of one window and then one of the surfaces of the secondwindow can still be problematic. However, by using different wedge types(e.g., flat surfaces angled at one edge for one window and a conicalwedge designed in the other window) in each of the two windows aspresented herein, better scrambling of the reflections internal to eachrespective optic and between the respective other wedged optical windoweven better aid in scrambling the reflections so as to minimize and evenin some cases substantially eliminate the overall “channel spectra”problem.

Thus, as part of the apparatus shown in FIG. 1, it is preferable thatone of the wedged windows is configured with both surfaces being flat(e.g., as denoted by references characters 20 in FIG. 2) and the otherhaving a flat surface 21 (as generally shown in FIG. 2) and anoff-center conic 22 (as also generally shown in FIG. 2) as the othersurface. Nonetheless, the configurations can also provide that both ofthe wedged windows be configured with flat surfaces angled with respectto each other to provide a first wedged window and a second wedgedwindow. It is to be noted however, that the windows described herein arenot limited to just optical wedged configurations despite suchconfigurations being optimal, as other configurations can also beimplemented without departing from the scope and spirit of theinvention.

In typical operation however, when the one of the windows is configuredwith a pair of flat surfaces angled with respect to each other toprovide a wedged optic (e.g., a first window 5′) the other window (e.g.,a second window 5) is most often configured nearest the detector 9 witha flat surface and an off-center conic surface wedged optic, wherein theflat surface of the second window is pointing toward (e.g., nearest) theoptical detector 9 and the off-center conic surface pointing toward(e.g., nearest) the sample, as generally shown in FIG. 1 and in greaterdetail in FIG. 2. However, other variations can also be utilized, suchas for example, having the wedged optic with the off-center conicsurface (e.g., first window 5′) pointing toward (e.g., nearest) theoptical source 12 and the flat surface pointing toward (e.g., nearest)the sample and the other optical wedged window (e.g., a second window 5with both surfaces being flat) being utilized nearest the detector 9.Thus, the wedge for a particular window can either be configured withboth surfaces being flat and angled (i.e., thicker at an edge) orprovided with a flat surface and an off-center conic surface of which iseasy to manufacture to provide the desired wedge, as described below.

To explain, FIG. 3A, FIG. 3B and FIG. 3C show the general concept ofmanufacturing a low cost off-center conical “wedge” via the utilizationof a larger window that is polished with a conical shape usingtechniques known in the art. For example, as shown in FIG. 3A, amanufactured high point 32 of a conic surface can be designed near thecenter of the larger window 30. By cutting out a window 34, as shown inFIG. 3A, that is smaller and off center of the high point 32, theresulting high point 32 for the particular optic (e.g., 34) is also offcenter. This aspect of moving the high spot off center in one window,(e.g., 5 or 5′, as shown in FIG. 1 and FIG. 2), as an examplearrangement, provides for a resultant optical wedge that is bestoptimized for scrambling of reflections that cause “channel spectra”.However, such a manufacturing technique wastes most of the material thatnonetheless results in a window 34 with a high point 32 to provideminimum path length which is important in the case of disposed samples,such as, but not limited to, water.

With respect to FIG. 3B and FIG. 3C, if smaller windows are desired, thepresent invention provides for 2, 3 (36, as shown in FIG. 3B) and even 4(38, as shown in FIG. 3C), or more (not shown) windows out of a singlemanufactured part. In this case the high point 32 is removed as waste sothe resulting windows have a high side and low side with a conical shapebut no sharp high point in the center. These shapes are different fromthe center high point window and are additionally beneficial inscrambling the optical effect that cause “channel spectra” Desirably, 3(FIG. 3B) or 4 (FIG. 3C) windows are good choices for low waste andlower manufacturing cost.

As a preferred embodiment, a desired application herein is to providethat only the lower window moves as data is collected to change pathlengths. The upper window, detector and the source optics thuspreferably, but not necessarily, do not move as data is collected toprovide the best possible stability in absorption measurements. Thus,moving only the lower window (e.g., moving between about 5 up to 10,000microns) to produce the optical path length changes allows the design ofthe motorized lower window drive system to be smaller, more rigid, morerepeatable, and lower in cost. The motorized drive system (i.e.,adjustable mechanism 14) needs to move the lower window 5′ up and downin a repeatable way with long term accuracy of only a few microns.Getting enough resolution in the drive system to have the ability tomove less than one micron per control step is not that difficult usingcurrent systems known to those skilled in the art. However, despite suchcurrent systems, there is still a need to calibrate the zero point wherethe windows touch and the optical path length is a minimum in field sothat the user can trust the measurement. Such a calibration stepprovides confidence to the user that the windows 5 and 5′, as shown bythe closed “operating” position in FIG. 1, touch (the minimum opticalpath length) so as to take into account normal wear, corrosion andtemperature changes in the mechanical stop and hinge assembly of thedetector arm 4.

This zero calibration can be done by several means. One is to place aliquid (e.g., water or alcohol) sample in the transmission cell and tomeasure the optical absorption as the windows are driven toward minimumoptical path length. If the absorption is measured every step of thetravel movement, the absorption will change (decrease) each step untilthe windows touch, then the absorption changes that were monitoredsuddenly decreases greatly. This sudden change in absorbance change perstep thus indicates the point at which minimum path length occurs.

Another method to calibrate optical path length is to measure the smallamount of optical channel spectra detectable with windows, such as thewindows described herein, of which are designed to ultimately remove thechannel spectra with samples but not completely with air. This opticalchannel signal is weak by design but it is a very accurate measure ofthe optical path length between the two windows if signals are averagedover an adequate amount of time, e.g., at about 60 seconds or longer.Such a method is beneficial in that the procedure can measure non zeropath lengths out to about 50 or more microns with excellent accuracyallowing not only the zero point to be measured but also all the shorterpath lengths.

As another beneficial alternative, a good zero calibration point methodthat is designed to be faster than the aforementioned process is toinsulate one of the mechanical stops and measure the sample arm stopcontact resistance electronically (i.e., a current measurement system).As the path length decreases to zero the windows touch and the arm islifted off the stop and the resistance of the stop contact jumps up.This can be measured on every sample run with very little or no addedtime.

Data Control System

It is to be appreciated that the method of operation or various selectedsteps thereof, can be carried out automatically by a system including acomputer or other electronic processor and computer program instructionstangibly embodied on a computer readable medium, such as a disk drive,magnetic tape, optical disk drive, memory card, etc. The computerreadable medium may perform as both an input and an output device.Optionally, the computer/processor may further be electronically coupledto one or more other output devices, such as display screens, printers,etc. and/or one or more other input devices, such as keyboards, internetconnections, etc.

In the system 100, the computer/processor (not shown) in an examplearrangement provides instructions to set the path length(s) for thesample therebetween the windows 5, 5′ to a certain value(s). Forexample, the computer/processor may automatically send instructions toset or change path lengths and collect optical information frominterrogated samples manipulated to provide various path lengths. If thesystem of FIG. 1 also includes a position sensor, such positioninformation may be returned to the computer processor to provide pathlength adjustments. The computer processor (not shown) also receiveselectronic signal information from the light detector 9 relating to theintensity (e.g., power) of light sensed by the light detector 9 aftertransfer of such light from the transmission cell section of FIG. 1, asdescribed above. The computer/processor may also automatically performthe calculations and evaluate the decisions provided by for example,software, graphical user input (GUI), etc., so as to direct stepsconfigured to guide a user. The computer processor (not shown) can alsoset the values of variables. The sequence of events performed by thecomputer/processor may be controlled in accordance with programinstructions stored on the computer readable medium and transferred tothe computer/processor therefrom. Results of the measurements may alsobe transferred from the computer/processor to the computer readablemedium for storage thereon. Output may also be provided to a user viaoutput devices. The user may control program execution via input devicesknown to those skilled in the art.

A preferred data collection control program method can be configured tooperate in the following way. First, the user can tell the program thatnew data collection is to be implemented. The program then prompts theuser to inspect and clean the windows, if needed. Then the user canlower the upper window and detector arm to the standard samplinglocation and the arm mechanism would signal the computer program thatthe arm is in the proper location for data collection to begin. Theprogram then signals the user that it is automatically collecting abackground spectrum. This spectrum can then be automatically analyzed tosee if the light collected had the expected characteristics, indicatingthat the window(s) 5, 5′ are clean and all is OK.

The user then can be prompted to raise the sample window detector arm 4and place a sample on the lower sample window 5′ (and optionally enter aname for next sample to be run). Upon verification, for example, by aposition sensor (not shown) that the arm 4 has been raised and loweredthe arm in a pattern that indicated that a sample was in place, thecontrol program can then automatically start the data collection cycle.

Data can be first collected with a large space between the samplewindows (or large optical path length). The motor is then directed(e.g., via software to include graphical user input (GUI) by a user,etc.) to raise the lower window 5′ to reduce the window spacing and pathlength and then collect more data. This process can be repeated aprogrammed number of times. As each set of data is collected dataanalysis can be started on the prior set of data.

The first analysis can be to check for the expected reductions in sampleabsorbance of the transmitted light. If the absorbance did not proceedaccording to Beers law the program can provide a signal to the user thatthere were likely air bubbles in the light beam and to check for amisplaced or undersized sample between the sample windows 5, 5′. As theprogrammed data collections take place, the program can then present thedata to the user who can interpret the data any number of ways. The usercan then manually pick the best path length, or run a program thatautomatically analyzes the data, etc.

As stated above, it is also possible with many samples to eliminate thebackground data collection and just use a Beers law and mathematicalmodel to interpolate over many different path lengths to build abackground spectrum of virtual zero path length which is useful in manydata analyses. This technique can lead to time saving when analyzingmany samples in a short period of time. Such a differential path lengthmeasurement technique is similar to the techniques described in U.S.Pat. Nos. 6,809,826 and 6,628,382.

The fast acting contact resistance position sensing system of thepresent embodiments also allows sample viscosity measurement as an addedfeature. The sample window is raised at a constant speed causing thesample thickness to be reduced at a constant speed. At some point theviscosity of the sample spreading out of the decreasing volume willcause enough force on the arm to lift it off of a configured mechanicalstop. This can often be indicated by an increase in contact resistance.The force on the sample arm is known, as is the speed of the windowmovement, and the sample thickness. Knowing these three items thusenables viscosity to be determined over a useful range. This informationcan be beneficially used to prevent air bubbles from being sucked intothe sampling light bean as the path length is increased at too high ofvelocity in later measurements where the path length is increased.

Control Software Strategy

The user presses a button to start a data collection cycle. The softwarecan then prompt the user to name the sample and to raise and inspect thewindow for cleanliness. After the windows are cleaned and inspected theuser can then label the sample as a background and then lower the samplearm starting the background collect.

The program can use background spectra to verify window cleanness. Ifthis background run is OK the user/or program can store the backgroundfor later use. The user can also label the sample and then place thesample into position. In most cases the sample can be a liquid that isplaced on the lower window with a pipette. An exemplary sample placed onthe window includes one of at least 500 microns thick because of surfacetension and viscosity. Therefore in most cases after the user has placedthe sample onto the lower window and then lowers the arm onto the samplethe sample will then fill the space between the upper and lower windows.

The user can look from the side and see that the sample has in factfilled the space between the windows, but the viewing of the sample inposition is difficult as the arm blocks most of the easy viewing angles.Therefore a program can be set up to automatically start collecting dataand look for air bubbles from misplaced samples after the arm has beenlowered to the standard lower sampling position.

The software can sense that the arm has been lowered and proceeds in thefollowing illustrative but non-limiting example steps: Step 1) Delay fora programmed time period (about 2 to 15 seconds to allow the detector tosettle after the light level change). Step 2) Start data collection forabout 5 to 15 seconds. Step 3) Decrease the space (optical path length)between the windows by 50% and collect more data. Step 4) Analyze thedata to see that the absorption has decreased by the expected amount ofabout 50%. If the absorption is not as expected the program could signalthe user that there appears to be air in the sample, or too littlesample in the window location. Step 5) If the absorption decreaseappears to be OK then the program can decrease the spacing (optical pathlength) by a programmed amount and collect and store a second data set.Step 6) Analyze data again for air bubbles and repeat and collect asmany different path lengths as programmed and Step 7) then signal theuser that the data collection is complete.

The discussion included in this application is intended to serve as abasic description. Although the present invention has been described inaccordance with the various embodiments shown and described, one ofordinary skill in the art will readily recognize that there could bevariations to the embodiments and those variations would be within thespirit and scope of the present invention. The reader should be awarethat the specific discussion may not explicitly describe all embodimentspossible; many alternatives are implicit. Such modifications and thelike are considered simple modifications that are well within theability of one of ordinary skill in the art and within the scope andspirit of the invention. Accordingly, many such modifications may bemade by one of ordinary skill in the art without departing from thespirit, scope and essence of the invention. Neither the description,drawings nor the terminology is intended to limit the scope of theinvention—the invention is defined by the claims.

The invention claimed is:
 1. An apparatus for measuring an opticalproperty of a sample, comprising: a first window and a second window,wherein the first window is configured to receive radiation from asource of optical energy over free space and the second window isconfigured with an incorporated optical detector that is utilized tooptically interrogate a disposed sample therebetween the pair ofwindows, wherein the first window and the second window are bothmoveable with respect to the positioning of the source of opticalenergy, and wherein the surfaces of the first window and the surfaces ofthe second window are further configured to respectively provide a firstoptical wedge and a second optical wedge so as minimize channel spectra,the first window being configured with a pair of flat surfaces angledwith respect to each other to provide the first optical wedge, and thesecond window being configured with a flat surface and an off-centerconic surface to provide the second optical wedge, the flat surface ofthe second window pointing toward the optical detector and theoff-center conic surface of the second window pointing toward thesample; and a computer adapted to control a separation betweenconfigured surfaces of the first window and the second window at avariable distance (P) in order to pull the disposed sample into a columncontained by surface tension or to squeeze the sample during opticalanalysis, wherein the computer is additionally configured to collect andstore information of different optical path lengths automatically of thepulled and/or squeezed sample(s).
 2. The apparatus according to claim 1,wherein the pair of windows are configured with a minimum dimension of0.005 millimeters (mm) up to a maximum dimension of up to 50 millimeters(mm).
 3. The apparatus according to claim 1, wherein the window havingthe incorporated optical detector is additionally coupled to amechanical stop configured with a contact resistance system that enablesthe processor to calibrate the point for minimum path length.
 4. Theapparatus of claim 1, wherein the computer controls the separationbetween the pair of windows by directing a motorized mechanism to move acoupled sample platform configured with one of the pair of windows. 5.The apparatus of claim 4, wherein the computer is configured toautomatically lower the sample platform to prevent damage to the pair ofwindows as an arm configured with one of the pair of windows is placeddown.
 6. The apparatus of claim 5, wherein the computer is furtherconfigured to thereafter direct the sample platform to raise and squeezethe sample.
 7. The apparatus of claim 1, wherein the computer is furtherconfigured to adjust optical path lengths of the sample by movement ofthe coupled sample platform over a range of lengths from 5 microns up to10,000 microns.
 8. The apparatus of claim 1, wherein at least one of thesurfaces of the first window and the second window comprises a conicalshape having a high side and low side with no sharp high point in thecenter.
 9. The apparatus of claim 1, wherein at least one of thesurfaces of the first window and the second window comprises a conicalshape with a manufactured high point.
 10. An apparatus for measuring anoptical property of a sample, comprising: a first window and a secondwindow, wherein the first window is configured to receive radiation froma source of optical energy over free space and the second window isconfigured with an incorporated optical detector that is utilized tooptically interrogate a disposed sample therebetween the pair ofwindows, wherein the first window and the second window are bothmoveable with respect to the positioning of the source of opticalenergy, and wherein the surfaces of the first window and the surfaces ofthe second window are further configured to respectively provide a firstoptical wedge and a second optical wedge so as minimize channel spectra,the first window and the second window each being configured with a pairof flat surfaces angled with respect to each other to respectivelyprovide the first optical wedge and the second optical wedge; and acomputer adapted to control a separation between configured surfaces ofthe first window and the second window at a variable distance (P) inorder to pull the disposed sample into a column contained by surfacetension or to squeeze the sample during optical analysis, wherein thecomputer is additionally configured to collect and store information ofdifferent optical path lengths automatically of the pulled and/orsqueezed sample(s).
 11. The apparatus according to claim 10, wherein thepair of windows are configured with a minimum dimension of 0.005millimeters (mm) up to a maximum dimension of up to 50 millimeters (mm).12. The apparatus according to claim 10, wherein the window having theincorporated optical detector is additionally coupled to a mechanicalstop configured with a contact resistance system that enables thecomputer to calibrate the point for minimum path length.
 13. Theapparatus of claim 10, wherein the computer controls the separationbetween the pair of windows by directing a motorized mechanism to move acoupled sample platform configured with one of the pair of windows. 14.The apparatus of claim 13, wherein the computer is configured toautomatically lower the sample platform to prevent damage to the pair ofwindows as an arm configured with one of the pair of windows is placeddown.
 15. The apparatus of claim 14, wherein the computer is furtherconfigured to thereafter direct the sample platform to raise and squeezethe sample.
 16. The apparatus of claim 10, wherein the computer isfurther configured to adjust optical path lengths of the sample bymovement of the coupled sample platform over a range of lengths from 5microns up to 10,000 microns.
 17. The apparatus of claim 10, wherein atleast one of the surfaces of the first window and the second windowcomprises a conical shape having a high side and low side with no sharphigh point in the center.
 18. The apparatus of claim 10, wherein atleast one of the surfaces of the first window and the second windowcomprises a conical shape with a manufactured high point.